My son's computer suddenly refused to boot into windows, hangs at the logo, refuses to do any automatic repair, refused to boot from usb (just hangs when OS\Installer should load, scratched my head about it for 2 days.
Then I unplugged 3 connected usb's (keyboard, mouse, wifi dongle - and it instantly booted as it should. Kinda annoying that windows does not show what's happening behind the scenes when it starts, because you have no idea what's causing the hang up.